I have a 94 Formula M6, car runs great and strong at start-up, and while cruising around, but the minute the temp starts to rise towards 200 it starts runnin like total crap, stutters and hesitates when you get on the throttle, but it runs great when cold, If I'm correct doesnt the engine start up and run in open loop until 160 or around? So maybe its somethin to do with that, I dunno - any suggestions?

Chris

 

Common problem for us with older LT1s. Scan it if you can. Problem is usually a sensor(O2, PCM temp. in water pump, IAC, TPS, etc.) Also check plugs and wires heat will build up resistance in wires and cause arcing, especially right off Idle. Also check egr. operation. All these problems can cause the same symptons, so sometimes it is tough to diagnose. Try to be systematic with your trouble shooting. I suggest starting with ignition, this seems most common cause of problems(plugs, wires, coil, ignition module, probably not opti if it is dry and works fine at all other times instead of off idle). Then start checking reference voltage at sensors to make sure there are no opens in sensor harnesses. Then start checking individual sensors. Eventually you can locate problem.

Good luck!!

 

Put a 160 thermostat in and don't worry about it getting to 200*

 

160 t-stat wont help. You have a closed loop problem. One the engine starts reading sensors to set oparating parameters there is a problem. You will still go into closed loop operation no matter what thermostat you run.

 

At least we assume it's a problem with going into closed loop. It's also possible it's heat soke with your ignition coil or possibly your plug wires for example. Only way to really know is get it scanned.

You can test the open/closed loop theory by unplugging your O2 sensors, this will force the car to stay in open loop at all times. If symptons go away then we know it is associated with closed loop.

 

the problem may be in the cat. if its breaking down it can clog as it heats up. causing escalating loss of power the longer you drive. but will run fine again after cooling off